1. Field of the Invention
The present invention relates generally to a mobile communication system supporting a multimedia service including voice and data services, and in particular, to a method and apparatus for controlling transmission power of control information used for processing data provided from a base station to a mobile station.
2. Description of the Related Art
An IS-2000 CDMA (Code Division Multiple Access) mobile communication system, a typical mobile communication system, supports only a voice service. However, with the development of communication technology and at the request of users, research has been carried out on a mobile communication system supporting a data service. For example, an HDR (High Data Rate) communication system has been proposed to support only a high-speed data service. The existing mobile communication systems are classified into a mobile communication system for supporting only the voice service and another mobile communication system for supporting only the data service. That is, although the mobile communication system is required to support both the voice service and the data service, the conventional mobile communication system is designed to support only one of the voice service and the data service. Consequently, there has been a long demand for a mobile communication system capable of supporting both the voice service and the data service. To meet the demand, a 1xEV-DV (Evolution in Data and Voice) mobile communication system has recently been proposed.
A mobile communication system supporting a multimedia service including a voice service and a data service includes a base station (BS) and a plurality of mobile stations (MSs) connected to the base station. Such a mobile communication system provides mobile stations (or users) with a voice service using the same frequency band, and provides the mobile stations with a data service by code division multiplexing (CDM). CDM is a technique for simultaneously providing a data service to a plurality of users at the same time period (e.g., slot). The mobile communication system includes a packet data channel (PDCH) for packet data transmission, and a packet data control channel (PDCCH), e.g., a secondary packet data control channel, for efficient transmission of packet data. The packet data channel is used to transmit packet data. Transmission of packet data over the air is performed in a physical layer packet (PLP) unit, and a length of the physical layer packet is varied at each transmission. The packet data control channel is used to transmit control information for enabling mobile stations or receivers to efficiently receive packet data. Typically, the control information includes a MAC ID (Medium Access Control Identifier) for user identification, and a last Walsh code index indicating a Walsh code to be used during a service among a plurality of Walsh codes provided by a base station.
Control information transmitted from a base station to mobile station over the packet data control channel undergoes power control. Conventionally, power control on the packet data control channel was independently performed, taking into consideration a channel environment of each mobile station. For example, among a plurality of mobile stations, a first mobile station receives first control information provided from the base station over a primary packet data control channel assigned thereto, and a second mobile station receives second control information provided from the base station over a secondary packet data control channel assigned thereto. If a channel environment of the first mobile station is poor, the base station performs a power control operation to increase power of the first control information. Likewise, if a channel environment of the second mobile station is poor, the base station performs a power control operation to increase power of the second control information. Such a power control operation is performed on the assumption that unique control information is provided to each mobile station.
Recently, in some cases, each mobile station of the mobile communication system consults not only the control information provided thereto but also control information provided to other mobile stations. This is to reduce the number of bits of control information transmitted from the base station, and efficiently use the control information. For example, if it is assumed that the number of Walsh codes provided from a base station is 32 and the number of Walsh codes to be used by a particular one of the mobile stations is 10, then the base station conventionally transmits all of the information indicating each of the 10 Walsh codes to the particular one of the mobile stations. However, recently, there has been proposed a method of transmitting only Walsh code space indicator information indicating some of the 10 Walsh codes. In this case, each mobile station consults not only its own Walsh code space indicator information but also Walsh code space indicator information for other mobile stations.
As stated above, when each mobile station of the mobile communication system processes received data by consulting not only the control information provided thereto, but also control information provided to other mobile stations, a new power control operation, different from the conventional power control operation, is required.